The physical constraints of integrated circuits do not allow for the inclusion of standard fixed resistors as used in non-integrated electrical circuits. However, in various applications, the use of resistors, or resistance devices, in an integrated circuit is beneficial.
As a result, various techniques have been employed in order to provide an electrical resistance device in an integrated circuit that may be manufactured during the process of manufacturing the integrated circuit device.
Most commonly, poly silicon was used to provide an electrical resistance in integrated circuit arrangements. Whilst this technique is feasible, poly silicon is limited in the range of electrical resistance it can present to the order of 1 to 3 kΩ's whilst at the same time consuming a relatively large region of silicon associated with widespread end resistance value.
Alternatively, active devices such as MOSFET devices have been used in a particular arrangement such that they present an electrical resistance between two nodes. Use of these devices has enabled the provision of electrical resistances in the order of 500 to 600 kΩ's.
Whilst the use of MOSFET devices resulted in a significant improvement with respect to the range of electrical resistance that could be generated in an integrated circuit, the arrangement of these devices requires that one node of the resistance device be coupled to ground, or the circuit substrate.
In various applications, there is a requirement for circuits with large time constants. As the ability to provide capacitive devices in integrated circuits is limited, there is a requirement for larger values of electrical resistance to satisfy the time constant requirements. Additionally, there is also a need for a high value electrical resistance device that has floating terminals.